Conventional internal combustion engines are well known and widely used in day-to-day life, these typically consisting of a cylinder, a crank, a connecting rod and a piston. These reciprocating piston engines are further designed with different capacities and for various applications using different types of fuels.
In an attempt to reduce “work loss” (this generally being defined to encompass any component of energy associated with the combustion cycle in the piston and valve arrangement and which is dissipated into some other form outside of output energy delivered to the vehicle crank) associated with such reciprocating piston engines, different types of engines have been produced, both with and without a reciprocating piston. Most notable among these are rotary engines.
One such well know effort is the Wankel engine, and which was designed with a rotary piston, that rotates continuously in one direction, thus reducing the losses which otherwise would have caused by the reciprocating motion of the piston in a conventional reciprocating piston internal combustion engine. In the Wankel engine, the four strokes of a typical Otto cycle occur in the space between a rotor, which is roughly triangular, and the inside of an associated housing, in the basic single-rotor Wankel engine, the oval-like housing surrounds a three-sided rotor. A central drive shaft, also called an eccentric shaft, passes through a center of the rotor, and is supported by bearings.
In operation, the rotor both rotates around an offset lobe (or crank) located on the eccentric shaft, thus creating orbital revolutions around the central shaft. Associated seals located at the corners of the rotor seal against the periphery of the housing, thus dividing it into three continuously moving combustion chambers. Fixed gears mounted on each side of the housing engage with ring gears attached to the rotor, and to ensure the proper orientation as the rotor moves.
During concurrent rotation and orbital revolution, each side of the rotor alternates in its position (i.e. closer and farther) relative to the wall of the housing, thus compressing and expanding the combustion chamber in a fashion similar to the strokes of a piston in a reciprocating engine, and with the power vector of the combustion stage traveling through the center of the offset lobe.
In contrast to a standard four stroke reciprocating piston engine producing one combustion stroke per cylinder for every two rotations of the crankshaft (that is, one half power stroke per crankshaft rotation per cylinder), each combustion chamber in the Wankel generates one combustion stroke per each driveshaft rotation, i.e. one power stroke per rotor orbital revolution and three power strokes per rotor rotation. Accordingly, the power output of the Wankel engine is generally higher than that of a four-stroke piston engine of similar physical dimension and size.
Wankel engines have several major advantages over reciprocating piston designs, in addition to having higher output for similar displacement and physical size, most notably including being considerably simpler with far fewer moving parts. The elimination of these parts not only makes a Wankel engine much lighter (typically half that of a conventional engine of equivalent power), but it also completely eliminates the reciprocating mass of a piston engine, with its internal strain and inherent vibration due to repeated acceleration and deceleration, thereby producing not only a smoother flow of power but also the ability to produce more power by running at higher revolutions per minute (rpm).
Corresponding disadvantages of Wankel style engines include, and in comparison to standard four cycle piston engines, the time available for fuel to be injected into the Wankel engine being significantly shorter, and again due to the way the three chambers rotate. Also, the fuel-air mixture cannot be pre-stored, as there is no intake valve and which means that, in order to obtain acceptable performance out of a Wankel engine, more complicated fuel injection technologies are required than for regular four-stroke engines. Also, the difference in intake times causes Wankel engines to be more susceptible to pressure loss at low RPM compared to regular piston engines. Also, and in terms of fuel economy, Wankel engines tend to be generally less efficient than four stroke piston engines.
Problems also occur with exhaust gases at a peripheral port exhaust, where the prevalence of hydrocarbon can be higher than from the exhausts of regular piston engines. Given the above considerations associated with Wankel engines, appropriate cooling and sealing have become very difficult and probably for these reasons the engine has not become very popular in industries.
An example of another type of rotary engine, drawn from the prior art, is set forth in U.S. Pat. No. 5,133,317, issued to Sakita, and which discloses a rotary piston engine incorporating a housing having a cylindrical shaped working chamber with inlet and exhaust ports. First and second piston assemblies are provided, each of which includes one or more pairs of diametrically wedge shaped pistons located within the working chamber. The piston assemblies rotate in a same direction and at recurrently variable speeds, such that one pair of diametrically opposite sub-chambers decreases in volume, with the other pair correspondingly increases in volume.
Reference is also made to the engine and drive system set forth in U.S. Pat. No. 6,691,647, issued to Parker, and which teaches an engine having four open-ended curved cylinders disposed in a toroidal arrangement with respect to a central pivot point. Two piston arms are pivoted about the central pivot point, the two arms carrying at opposite ends of each a total of four pistons. Each piston exhibits two faces and, in mounting on the piston arm ends, faces tangentially one away from the other for alternate engagement with adjacent ends of two of the cylinders.
Gas turbine technology is another type of non-reciprocating piston engine application and which is in fairly wide use, although not presently in most vehicular applications. A gas turbine extracts energy from a flow of hot gas produced by combustion of gas or fuel oil in a stream of compressed air. Turbines typically incorporate an upstream air compressor (radial or axial flowing), and which is mechanically coupled to the downstream turbine (this also generally defined by a plurality of radially extending and centrifugally driven blade element), with a combustion chamber in between.
In this fashion, energy is released when compressed air is mixed with fuel and ignited in the combustion chamber. The resulting gases are directed over the turbine's blades, thereby spinning the turbine and mechanically powering the compressor. In a final step, the gases are passed through a nozzle, generating additional thrust by accelerating the hot exhaust gases by expansion back to atmospheric pressure.
Energy from a turbine engine is extracted in the form of shaft power, compressed air and thrust, in any combination, and used to power such as aircraft, trains, ships, electrical generators and, in regards to land operated vehicles, such as military tanks. Given that gas turbines exhibit very high values of power to weight ratio, and work most efficiently at very high speeds, this renders them for the most part not practical in use with automobiles.